This invention relates to liquid level sensors and especially to conductive multilevel sensing systems that are cost effective.
The electrolytic conductivity probe has been used as a liquid level detector for many years. The basic device consists of a conducting rod mounted on an insulated support and extending down to the level to be detected. The rod is connected to an electronic detector unit which supplies a small electrical potential to the rod and senses when the rod is short-circuited by the rising liquid. The electronic unit usually contains a relay to switch on motors, alarms, etc. A detector of this type for blind people is described by R. Roberts and G. Jernakoff in U.S. Pat. No. 3,781,840 and has discrete transistors or amplifiers as signal detectors.
For single level sensing, a device using a discrete detector and an electrical probe similar to the one in this patent is suitable. However, it is not the most cost efffective way of implementing a multilevel detector due to the number of components required and the potential complexity of packaging the device. Furthermore, protection should be provided for the electrical probe when the liquid to be sensed is chemically corrosive.